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Common Summertime Myths

ELEVATION MATTERS: The sun’s UVB rays are 18 percent stronger at lake level than at sea level, and increase three percent for every 1,000 feet in elevation gain. UVB rays are responsible for sunburns and are a major contributor to skin cancer. Creative Family/bigstockphoto.com

I remember sitting poolside with my friends, as a kid, enduring that tortuous hour after eating until we could finally jump back in the water. Get in any sooner, the adults warned, and we might cramp up and drown.

The advice was repeated so often, we thought it had to be true. But was it? Here’s a look at the facts behind a number of common summertime myths, particularly those affecting us here in Tahoe where the humidity is low, the UV rays are strong, and everyone is recreating in the glorious outdoors.

You should wait an hour after eating before swimming.

False. Parents, you can stop torturing your kids. The theory behind this claim is that when blood is diverted to your digestive organs, your muscles will be deprived and more likely to cramp. But there’s no evidence to back this up. Cramps can happen when you swim, but they’re not related to your ham sandwich.

Your body adapts to hot weather.

True. To help you endure the heat, your sweat glands get larger, your body temperature rises more slowly, and your heart rate stays lower at a given workload. You’ll sweat more volume and begin sweating at a lower core temperature, allowing you to stay active without overheating.

These adjustments mostly happen in the first five days of heat exposure, but it takes about two weeks to fully acclimate. The fitter you are, and the more you exercise in the heat, the faster you’ll adjust.

SPF 30 sunscreen blocks twice as much sun as SPF 15.

False. It’s important to know that the SPF rating applies only to UVB rays, and that the increase in protection from SPF 15 to 30 (and beyond) is not linear. SPF 15, for example, blocks 93 percent of UVBs, but doubling the SPF to 30 blocks only 97 percent. With SPF 50, you get just one percent more blockage.

So why the big range in SPFs? Theoretically, the higher the number, the longer you’re protected. But since most people don’t apply enough sunscreen to begin with, and then engage in activities that remove it, like swimming, sweating, and toweling off, the best way to protect yourself is to goop up every two hours, regardless of SPF.

False. To carry the “broad spectrum” label, the FDA requires only that UVA protection increase proportionally as SPF rises. So, SPF 45 will block more UVA rays than SPF 15, but you don’t know how much protection you’re actually getting. What’s more, one company’s broad-spectrum product could offer much less UVA protection than another’s, even when their SPF numbers are identical.

Sunscreen protects you as soon as it’s applied.

It depends on the product. Sunscreens fall into two categories; chemical and physical. Chemical sunscreens, like avobenzone and oxybenzone, need 20 to 30 minutes to bind to proteins in your skin before becoming effective. Physical sunscreens, containing zinc oxide or titanium dioxide, work by reflecting rays off your skin’s surface, and are effective as soon as you apply them.

Caffeine dehydrates you.

False. This myth just won’t die. Even the American College of Sports Medicine (ACSM) says that caffeinated drinks do not cause dehydration. Studies show that people can stay perfectly well hydrated, whether their drink of choice is soda, diet soda, coffee, juice, carbonated water, or plain water. Caffeine can make you pee more frequently, but you’re not losing more water than you take in.

If you exercise in the heat, you need a sports drink.

Maybe, depending on the length and intensity of your workout. For sessions under an hour, the ACSM says plain water is all you need; your body has adequate stores of glycogen and electrolytes for that period of time.

But sustained workouts lasting more than an hour warrant replacement of carbs and electrolytes. Sports drinks provide these ingredients conveniently, but many commercial products are high in sugar and contain artificial dyes and artificial sweeteners. Specialty waters and energy drinks may provide vitamins and caffeine, but can lack the electrolytes and carbs you need for a long workout.